Road waviness and the dynamic tyre force

Abstract

The paper analyses influence of random road profile waviness on the dynamic load of roads. The standard ISO 8608 (1995) assumes equal unevenness intensity in short and long wave bands in the road profile power spectral density (PSD), i.e. waviness parameter w = 2. In reality differences between intensity of unevenness in wave bands have been observed on about 40% of measured roads. For simulation of the dynamic tyre force response the quarter car model is used. All combinations of non-standard displacement PSDs with waviness varied from 1.5 to 2.5 are examined. Fractal structure of the PSD with different waviness for short and long waves is considered. Three alternatives of reference PSD are investigated: i) reference with constant parameters, independent of the analysed PSD, ii) reference obtained by straight-line fitting of analysed PSD, iii) reference with the same variance of displacement as the analysed PSD. The results show that the straightforward use of profile displacement PSD with constant waviness parameter w = 2 could sometimes significantly affect the predicted vehicle random response.